Projection scan multi-touch sensor array

ABSTRACT

A touch sensor panel can be constructed on a single surface of a substrate. The panel can be formed as a plurality of distributed RC lines arranged in an array of rows and columns. Each distributed RC line can include alternating connected transistors and metal pads formed on a single surface of the substrate. During operation, the rows and columns are enabled at different times, and the pulse travel times for each row and column in both directions are measured. Equalized travel times are then computed as the sum of the pulse travel times in both directions, and indicate which rows and columns have a finger touching it. The un-equalized pulse travel time data can then be used to determine the relative positions of the fingers within the rows and columns and un-ambiguously determine the positions of all the finger contacts.

FIELD OF THE INVENTION

This invention relates to touch sensor panels, and more particularly, tomulti-touch sensor panels whose elements can be applied to a singlesurface of a substrate.

BACKGROUND OF THE INVENTION

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, touch panels, joysticks, touch screens and the like. Touchscreens, in particular, are becoming increasingly popular because oftheir ease and versatility of operation as well as their decliningprice. Touch screens can include a touch panel, which can be a clearpanel with a touch-sensitive surface. The touch panel can be positionedin front of a display screen so that the touch-sensitive surface coversthe viewable area of the display screen. Touch screens can allow a userto make selections and move a cursor by simply touching the displayscreen via a finger or stylus. In general, the touch screen canrecognize the touch and position of the touch on the display screen, andthe computing system can interpret the touch and thereafter perform anaction based on the touch event.

Touch panels can include an array of touch sensors capable of detectingtouch events (the touching of fingers upon a touch-sensitive surface).Some current touch panels are able to detect multiple touches (thetouching of fingers upon a touch-sensitive surface at distinct locationsat about the same time) and near touches (fingers within the near-fielddetection capabilities of their touch sensors), and identify and tracktheir locations. Examples of multi-touch sensor panels are described inApplicant's co-pending U.S. application Ser. No. 10/842,862 entitled“Multipoint Touchscreen,” filed on May 6, 2004 and published as U.S.Published Application No. 2006/0097991 on May 11, 2006, the contents ofwhich are incorporated by reference herein.

Capacitive touch sensor panels can be formed as an array of rows andcolumns of sensors on opposing sides of a touch substrate. For example,the rows can form drive electrodes on one surface of the touch substrateand the columns can form sense electrodes on the opposing surface. Toscan a sensor panel, a stimulus can be applied to one row with all otherrows held at DC voltage levels. When a row is stimulated, a modulatedoutput signal can appear on the columns of the sensor panel. The columnscan be connected to analog channels (also referred to herein as eventdetection and demodulation circuits). For every row that is stimulated,each analog channel connected to a column generates an output valuerepresentative of an amount of change in the modulated output signal dueto a touch event occurring at the sensor located at the intersection ofthe stimulated row and the connected column. After analog channel outputvalues are obtained for every column in the sensor panel, a new row isstimulated (with all other rows once again held at DC voltage levels),and additional analog channel output values are obtained. When all rowshave been stimulated and analog channel output values have beenobtained, the sensor panel is said to have been “scanned,” and acomplete “image” of touch can be obtained over the entire sensor panel.This image of touch can include an analog channel output value for everypixel (row and column) in the panel, each output value representative ofthe amount of touch that was detected at that particular location.

The manufacturing cost of a two-surface sensor panel as described aboveis generally higher than if only one surface of the substrate was neededfor sensor circuitry. In addition, when the touch substrate overlays adisplay device (e.g., an LCD), circuitry on the second surface typicallyincreases light loss as compared to a single surface system. Therefore,it is desirable for cost and performance reasons to realize amulti-touch sensor that only needs one surface of the touch substratefor sensor circuitry.

SUMMARY OF THE INVENTION

A multi-touch sensor panel can be constructed on a single surface of atouch substrate to reduce manufacturing costs and minimize light loss intransparent embodiments. The panel can be formed as a plurality ofdistributed RC lines arranged in an array of rows and columns. Eachdistributed RC line can include alternating connected transistors andmetal pads formed on a single surface of a sensor panel substrate, withthe drain and source terminals of the transistors connected to adjacentmetal pads.

During operation, the rows and columns are enabled at different times,and the pulse travel times for each row and column in both directionsare measured. Equalized travel times for each row and column are thencomputed as the sum of the pulse travel times in both directions. Theequalized pulse travel times can be compared to an equalized no-touchpulse travel time to determine which rows and columns, if any, have afinger touching it. The equalized pulse travel times represent a map,albeit an ambiguous one, of all points touched by fingers. However,before an unambiguous map of finger contacts can be generated, moreinformation needs to be applied. The reason for this is that theequalized pulse travel times, which provide high selectivity indetermining whether a finger(s) is touching over a row or a column, onlyprovide projection scan-like data that, by itself, cannot resolverotational ambiguity of multiple finger contacts.

However, once the rows and columns containing finger contacts are known,the un-equalized left-to-right, right-to-left, top-to-bottom andbottom-to-top pulse travel time data can be used to determine therelative positions of the fingers within the rows and columns andun-ambiguously determine the positions of all the finger contacts. Inparticular, for each row indicating a possible contact, the pulse traveltimes for right-to-left and left-to-right are compared against otherrows for which there were possible contacts, one by one, to establishthe relative positions of the contacts across the rows. After all rowshave been processed, the same process is then repeated for each columnshowing a possible contact. For each column indicating a possiblecontact, the pulse travel times for top-to-bottom and bottom-to-top arecompared against other columns for which there were possible contacts,one by one, to establish the relative positions of the contacts acrossthe columns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary distributed resistor-capacitor (RC) lineaccording to one embodiment of this invention.

FIG. 2 illustrates how an exemplary distributed RC line can serve as atouch sensor according to one embodiment of this invention.

FIG. 3 illustrates an exemplary metal pad and thin film transistor(TFT), which are examples of the basic circuit elements needed toconstruct a distributed RC line according to one embodiment of thisinvention.

FIG. 4 illustrates an exemplary distributed RC line constructed fromdiscrete resistors, capacitors, and metal pads that can represent onerow of multi-touch sensors according to one embodiment of thisinvention.

FIG. 5 illustrates an exemplary distributed RC line constructed usingmetal pads and field effect TFTs according to one embodiment of thisinvention.

FIG. 6 illustrates an exemplary circuit capable of measuring pulsetravel times to allow for equalization of the spatial dependency of thepulse travel times according to one embodiment of this invention.

FIG. 7 is a plot of exemplary pulse travel times for a finger touching adistributed RC line at various points along the line according to oneembodiment of this invention.

FIG. 8 is an exemplary plot showing the sensitivity of the pulse traveltime as a function of the ratio of finger capacitance to thecompartmental (background) capacitance, C_(i), of the distributed RCline according to one embodiment of this invention.

FIG. 9 illustrates an exemplary four row and four column multi-touchsensor panel constructed with an array of one-dimensional distributed RClines according to one embodiment of this invention.

FIG. 10 illustrates two exemplary cases where the projection scan-likedata requires disambiguation according to one embodiment of theinvention.

FIG. 11 is a flowchart of a process for disambiguating the initialcontact map according to one embodiment of this invention.

FIG. 12 illustrates an exemplary block diagram of a projection scanmulti-touch sensor panel and related components according to oneembodiment of this invention.

FIG. 13 a illustrates an exemplary mobile telephone that can include asingle-surface multi-touch sensor panel according to one embodiment ofthis invention.

FIG. 13 b illustrates an exemplary digital audio/video player that caninclude a single-surface multi-touch sensor panel according to oneembodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of preferred embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the preferred embodiments of the presentinvention.

A multi-touch sensor panel can be constructed on a single surface of atouch substrate to reduce manufacturing costs and minimize light loss intransparent embodiments. The panel can be formed as a plurality ofdistributed RC lines arranged in an array of rows and columns. Eachdistributed RC line can include alternating connected transistors andmetal pads formed on a single surface of a sensor panel substrate, withthe drain and source terminals of the transistors connected to adjacentmetal pads. The substrate can constructed from a variety of differentmaterials including, but not limited to, metal, plastic, and glass.Because the single-surface elements of the sensor panel can bemanufactured using a printing process (e.g., roll-to-roll or offset),manufacturing costs can be lower as compared to systems produced via abatch process. Transparent multi-touch substrates may also be suitableas an overlay on a display device such as an LCD display, and thepresence of elements on only a single side of the substrate can resultin less light loss.

FIG. 1 illustrates an exemplary distributed resistor-capacitor (RC) line100. A distributed RC line 100 as shown in FIG. 1 delays the propagationof an electrical pulse by an amount that depends on the magnitude of theproduct RC, where R is the total resistance of all resistive elementsand C is the total capacitance of all capacitive elements making up thedistributed RC line. The magnitude of RC can be found by measuring thetime it takes a pulse that enters the left (or the right side) to appearon the opposite side. Any change in the value of R or C (and thus theproduct of R and C), either globally or locally, alters the time ittakes a pulse to travel from one end to the other of distributed RC line100. Because a finger has an inherent capacitance that can change theoverall capacitance of distributed RC line 100, such distributed RClines can be the basis for a capacitive touch sensor.

FIG. 2 illustrates how an exemplary distributed RC line 200 can serve asa touch sensor. It should first be understood that with reasonablyconstant values for R and C, the pulse travel time from one end of theline to the other is relatively constant. However, when a conductingobject such as finger 202 approaches distributed RC line 200, thecapacitance of the line near the finger changes. This causes the pulsetravel time to change. While the location of finger 202 alongdistributed RC line 200 can be inferred by comparing the pulse traveltime to a known pulse travel time profile, this methodology isimpractical to implement because it would be difficult to create a pulsetravel time profile for all possible values of finger capacitance.Furthermore, such a methodology could not identify the presence of asecond finger along distributed RC line 200.

FIG. 3 illustrates an exemplary metal pad 300 and thin film transistor(TFT) 302, which are examples of the basic circuit elements sufficientto construct a distributed RC line according to embodiments of thisinvention. Metal pad 300 can be square and of sufficient size to providegood spatial resolution for determining the position of a touchingfinger overlaying an array of closely spaced metal pads, but shapesother than squares also be used. Metal pad 300 can be transparent oropaque. TFT 302 can be a low mobility device such as an organictransistor.

FIG. 4 illustrates an exemplary distributed RC line 400 constructed fromdiscrete resistors 402, capacitors 404, and metal pads 406 that canrepresent one row of multi-touch sensors. However, because the use ofdiscrete resistors 402 would not enable the construction of atwo-dimensional multi-touch sensor array as required for a multi-touchsensor panel, low mobility transistors can be used instead of discreteresistors 402.

FIG. 5 illustrates an exemplary distributed RC line 500 constructedusing metal pads 502 and field effect TFTs 504 according to someembodiments of the invention. In the usual applications where TFTs areemployed (e.g., LCDs), they are designed to operate as switches with alow on-state resistance. In other words, when the enable line ENB isasserted, TFTs 504 conduct and metal pads 502 are essentially connectedto each other, and when ENB is de-asserted, the TFTs are not conductingand the metal pads are essentially isolated from each other. However,TFTs 504 utilized with embodiments of this invention may have a highon-state resistance and act as resistors. The TFTs also provide anintrinsic capacitance.

Note that organic TFTs (used in display devices and plasticrollable/foldable products) typically have very low mobility μ (i.e.,high on-state resistance) compared to silicon-based TFTs, and aretherefore usually considered “poor” transistors. However, low mobilityis a preferred characteristic for embodiments of this invention. Becauseorganic TFTs have low mobility and are easy to manufacture (they can beprinted, painted or rolled on surfaces without stringent clean roomrequirements), the TFTs used with some embodiments of this invention canbe organic TFTs. However, in other embodiments, silicon-based TFTs orother transistors fabricated with sufficiently low mobility can also beused.

As shown in FIG. 5, the gate terminals G of TFTs 504 are connectedtogether and driven by ENB. TFTs 504 turn on when a DC voltage isapplied to ENB. A voltage pulse Vstim entering either the right or leftside of the row causes TFTs 504 to conduct. As each TFT 504 transitionsfrom an off-state to an on-state it passes through a saturation regionwhere it has very high resistance. As each TFT 504 enters a linearregion its resistance decreases and can be approximated using theShockley model, which expresses the drain current asI _(d)=(μCW/L)(V _(gs) −V _(th))V _(ds)−(½)V _(ds) ²,where μ is the mobility, C is the gate unit capacitance, W is thetransistor width, L is the transistor length, V_(gs) is the gate sourcevoltage, V_(th) is the threshold voltage, and V_(ds) is the drain sourcevoltage. Because there is only a capacitive load along the distributedRC line, V_(ds) can be assumed to be small. Therefore, the effectiveresistance can be written as

$R_{eff} = {\frac{L}{\left( {\mu\;{CW}} \right)\left( {V_{gs} - V_{th}} \right)}.}$

When ENB is asserted, TFTs 504 are in their on state and present a highresistance R between metal pads 502. Each metal pad 502 is capacitivelycoupled to the AC ground provided by the ENB voltage source through theTFT's source-gate capacitance. The capacitance C can also be made up ofstray components to other grounds. The magnitude of C should preferablybe less than the capacitance introduced by a touching finger in orderfor distributed RC line 500 to have sufficient resolution to be aneffective touch sensor. The large TFT resistance R coupled with a smallpad capacitance C produces a sufficiently large pulse travel time thatcan be measured with a low-cost microcontroller.

As mentioned above, the pulse travel time depends on the product RC. Afinger touching or in close proximity to distributed RC line 500 altersthe product RC and thus its presence will increase the pulse traveltime. However, because distributed RC line 500 has a distributedresistance and capacitance, the pulse travel time will also depend onwhere the finger is located along the distributed RC line. For example,a finger touching near one end of distributed RC line 500 will result ina different pulse travel time than the same finger touching the centerof the distributed RC line. For multi-touch sensing according toembodiments of this invention, this effect should be equalized so thatno matter where the finger is located along distributed RC line 500, thepulse travel time will be approximately the same. In order to equalizethis spatial dependency, two measurements can be taken. For the firstmeasurement, a Vstim pulse is injected into the right side of the lineand the pulse travel time is recorded. For the second measurement, aVstim pulse is injected into the left side and the travel time is onceagain recorded. Summing the two measurements equalizes the spatialdependency.

FIG. 6 illustrates an exemplary circuit capable of measuring pulsetravel times to allow for equalization of the spatial dependency of thepulse travel times according to embodiments of this invention. FIG. 6includes distributed RC line 600 with the TFTs symbolically replacedwith resistors R and capacitors C. In FIG. 6, left side driver 602 isenabled while right side driver 604 is disabled. The enabled left-sidedriver 602 injects a pulse Vstim into the left side of distributed RCline 600, and the time at which the pulse was injected is recorded. Whenthe amplitude of the exiting pulse 606 on the right side reaches athreshold voltage Vth, the right side voltage comparator 608 changesstate. The arrival time of the pulse as indicated by the comparator'sstate change can be recorded by a conventional digital timer circuit(not shown). Note that in other embodiments, circuits other thancomparators can be used to detect the arrival of the pulse. Thedifference between the pulse injection time and the arrival time is thepulse travel time going left to right. This process is repeated but withright side driver 604 now enabled and left side driver 602 disabled,which produces a pulse exiting from comparator 610 and a pulse traveltime going right to left. The sum of these two measurements is theequalized pulse travel time.

FIG. 7 is a plot of exemplary pulse travel times for a finger touching adistributed RC line at various points along the line according toembodiments of the invention. Trace 704 represents pulse travel timesfor the pulse going left to right while trace 702 is for the pulse goingright to left. Note that the pulse travel time changes significantly asa function of finger position, and thus the location of a fingertouching a single sensor can be determined from comparing theleft-to-right and right-to-left pulse travel times. The equalized traveltime is shown as trace 706, which is substantially independent of fingerposition. Its profile (general shape) is also independent of the actualcapacitance added by the finger. Therefore, if two or more fingers weretouching the distributed RC line, the magnitude of the travel timeswould change (increase) but the profile would remain relatively flat.Trace 708 represents the equalized travel time for the case when nofinger is touching the distributed RC line. Therefore, any measuredpulse travel times in excess of trace 708 indicates that one or morefingers are touching the distributed RC line.

FIG. 8 is an exemplary plot showing the sensitivity of the pulse traveltime as a function of the ratio of finger capacitance to thecompartmental (background) capacitance, C_(i), of the distributed RCline. The plot shows that the difference in travel times for the touchedversus the untouched cases depends on the ratio of finger capacitance tocompartmental (baseline) capacitance. Larger capacitance ratios providebetter differentiation between the touched and the untouched cases. Ifthe ratio becomes too small then the temporal resolution of the pulsetravel time measurement will have to increase.

FIG. 9 illustrates an exemplary four row and four column multi-touchsensor panel 900 constructed with an array of one-dimensionaldistributed RC lines according to embodiments of this invention. Duringoperation, the rows and columns are enabled at different times, and theleft-to-right and right-to-left pulse travel times and equalized traveltimes for each row and column are measured or computed. For example, tomeasure the row left-to-right pulse travel times, the left sideterminals (LR0-3) can be connected to one or more pulse drivers whilethe right side terminals (RR0-3) can be connected to individual timecapture circuits through individual comparators. The ENB_ROWS signal canbe asserted and the ENB_COLS signal is negated. A pulse is the injectedinto each left side terminal and the pulse travel time for each row isrecorded. Note that these row travel time measurements may be performedsimultaneously for two or more rows. This process can then be repeatedto capture right-to-left pulse travel times. When the equalized pulsetravel times for the rows have been computed, they can be compared tothe equalized no-touch travel time to determine which rows, if any, havea finger touching it.

The above-described process can be repeated for the columns. TheENB_COLS signal can be asserted and the ENB_ROWS signal is negated.Pulses are injected into the top terminals (TC0-3) (in some embodimentsa single pulse for each column), and the pulse travel times for top tobottom pulse injection are recorded. This is repeated for bottom to toppulse injection. The resulting equalized pulse travel times for thearray of columns provides an indication as to which columns have afinger touching it. The combined row and column data is a map, albeit anambiguous one, of all points touched by fingers. However, before anunambiguous map of finger contacts can be generated, more informationneeds to be applied.

Using just the equalized pulse travel times does not allow for anunambiguous construction of a map of finger contacts. The reason forthis is that the equalized pulse travel times, which provide highselectivity in determining whether a finger(s) is touching over a row ora column, only provide projection scan-like data that, by itself, cannotresolve rotational ambiguities of multiple finger contacts. However,once the rows and columns containing finger contacts are known, theun-equalized left-to-right, right-to-left, top-to-bottom andbottom-to-top pulse travel time data can be used to determine therelative positions of the fingers within the rows and columns andun-ambiguously determine the positions of all the finger contacts.

It should be understood that although the single-surface multi-touchsensor panel shown in FIG. 9 is formed in rows and columns perpendicularto each other, in other embodiments other non-orthogonal orientationsare possible. For example, in a polar coordinate system, the “rows” canbe concentric circles and the “columns” can be radially extending lines(or vice versa). It should be understood, therefore, that the terms“row” and “column,” “first dimension” and “second dimension,” or “firstaxis” and “second axis” as may be used herein are intended to encompassnot only orthogonal grids, but the intersecting traces of othergeometric configurations having first and second dimensions (e.g. theconcentric and radial lines of a polar-coordinate arrangement).

As mentioned above, the pulse travel time depends on the position of thefinger along the distributed RC line. Therefore, the four measurementsof pulse travel times for each row and for each column can be comparedto each other to resolve rotational ambiguities. For example, FIG. 10illustrates two exemplary cases where the projection scan-like datarequires disambiguation according to embodiments of the invention. Inthe exemplary 8×8 array of FIG. 10, two finger contacts are shown. Inthe array on the left, the fingers are located at (1, 5) and (2, 6). Inthe array on the right the fingers are located at (2, 5) and (1, 6).

The equalized pulse travel time data for both cases shown in FIG. 10 isbasically identical. Therefore, the equalized pulse travel time dataalone is not sufficient to distinguish the touching pattern shown on theleft frame from the touching pattern shown on the right. In other words,the equalized pulse travel time data can be used to determine thatcontacts were detected in rows 1 and 2 and columns 5 and 6, but eithercontact pattern in FIG. 10 could have caused that result. For example,suppose in FIG. 10 that the actual touching pattern is identical to thatshown in the left frame of FIG. 10. Nevertheless, the equalized pulsetravel times suggest that there are four possible contacts as shown inthe following table. These possible contacts represent the initialcontact map, which is made up of real and non-existent contacts.

Possible contacts (1, 5) (1, 6) (2, 6) (2, 5) Actual contacts (1, 5) (2,6)

In embodiments of the invention, the raw pulse travel time data can beused to eliminate the nonexistent contacts. FIG. 11 is a flowchart of aprocess for disambiguating the initial contact map according toembodiments of this invention. Step 1100 indicates the start of theprocessing of the rows in the sensor panel. For each row indicating apossible contact, the pulse travel times for right-to-left andleft-to-right are compared against other rows for which there werepossible contacts, one by one, to establish the relative positions ofthe contacts across the rows. Thus, in step 1102, the right-to-leftpulse travel time for row “i” is compared to the right-to-left pulsetravel time for row “j”. If the right-to-left pulse travel time for row“i” is larger than the right-to-left pulse travel time for row “j”, thenit is possible that the row “i” contact is left of the row “j” contact(see step 1104). If not, then it is possible that the row “j” contact isleft of the row “i” contact (see step 1106). Next, in step 1108, theleft-to-right pulse travel time for row “i” is compared to theleft-to-right pulse travel time for row “j”. If the left-to-right pulsetravel time for row “i” is larger than the left-to-right pulse traveltime for row “j”, then it is possible that the row “i” contact is rightof the row “j” contact (see step 1110). If not, then it is possible thatthe row “j” contact is left of the row “i” contact (see step 1112). Theresults of steps 1102 and 1108 can be interpreted as shown in the tablebelow.

Step 1108-Yes Step 1108-No Step 1102-Yes Undefined Contact in row “i” ina column to the left of contact in “row “j” Step 1102-No Contact in row“i” in Contact in row “i” in a column to the right same column as ofcontact in row “i” contact in row “j”

After all rows have been processed (see step 1114), the same process isthen repeated for each column showing a possible contact (see step1116). For each column indicating a possible contact, the pulse traveltimes for top-to-bottom and bottom-to-top are compared against othercolumns for which there were possible contacts, one by one, to establishthe relative positions of the contacts across the columns. Thus, in step1118, the top-to-bottom pulse travel time for column “k” is compared tothe top-to-bottom pulse travel time for column “m”. If the top-to-bottompulse travel time for column “k” is larger than the top-to-bottom pulsetravel time for column “m”, then it is possible that the column “k”contact is below the column “m” contact (see step 1120). If not, then itis possible that the column “m” contact is below the column “k” contact(see step 1122). Next, in step 1124, the bottom-to-top pulse travel timefor column “k” is compared to the bottom-to-top pulse travel time forcolumn “m”. If the bottom-to-top pulse travel time for column “k” islarger than the bottom-to-top pulse travel time for column “m”, then itis possible that the column “k” contact is above the column “m” contact(see step 1126). If not, then it is possible that the column “m” contactis above the column “k” contact (see step 1128). The results of steps1118 and 1124 can be interpreted as shown in the table below.

Step 1124-Yes Step 1124-No Step 1118-Yes Undefined Contact in column “k”in a row below contact in “column “m” Step 1118-No Contact in columnContact in column “k” in a row above “k” in same row as contact incolumn contact in column “m” “m”

Thus, after disambiguating all rows and columns using the algorithmdefined in FIG. 11, the actual contact locations can be determined.

FIG. 12 illustrates an exemplary block diagram 1200 of projection scanmulti-touch sensor panel 1202 and associated components according to oneembodiment of this invention. Panel 1202 can be driven with Vstimthrough left-to-right drivers 1204 selectable by an ENB_LR enablesignal, right-to-left drivers 1206 selectable by an ENB_RL enablesignal, top-to-bottom drivers 1208 selectable by an ENB_TB enablesignal, and bottom-to-top drivers 1210 selectable by an ENB_BT enablesignal. The enable rows signal ENB_ROWS can be generated by gatingENB_RL and ENB_LR through OR gate 1212, while the enable columns signalENB_COLS can be generated by gating ENB_TB and ENB_BT through OR gate1214. Microprocessor 1216 can generate ENB_RL, ENB_LR, ENB_TB, ENB_BT,Vstim, and a multiplex select signal Sel_Mux. When the rows or columnsare enabled and a pulse on Vstim is sent through panel 1202, multiplexer1218 selects one group of outputs (RL, LR, TB and BT) from panel 1202 inaccordance with Sel_Mux, detects the pulse using comparator 1220 andthreshold Vth, where it is captured back in microprocessor 1216, whichcan then compute the total delay time for that pulse.

Microprocessor 1216 can also be communicatively coupled to a hostprocessor (not shown) for performing actions based on the outputs ofpanel 1202 that can include, but are not limited to, moving an objectsuch as a cursor or pointer, scrolling or panning, adjusting controlsettings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral deviceconnected to the host device, answering a telephone call, placing atelephone call, terminating a telephone call, changing the volume oraudio settings, storing information related to telephone communicationssuch as addresses, frequently dialed numbers, received calls, missedcalls, logging onto a computer or a computer network, permittingauthorized individuals access to restricted areas of the computer orcomputer network, loading a user profile associated with a user'spreferred arrangement of the computer desktop, permitting access to webcontent, launching a particular program, encrypting or decoding amessage, and/or the like. The host processor can also perform additionalfunctions that may not be related to panel processing, and can becoupled to program storage and a display device such as a liquid crystaldisplay (LCD) for providing a UI to a user of the device.

FIG. 13 a illustrates an exemplary mobile telephone 1336 that caninclude single-surface multi-touch sensor panel 1324 according toembodiments of this invention. FIG. 13 b illustrates an exemplarydigital audio/video player 1338 that can include single-surfacemulti-touch sensor panel 1324 according to embodiments of thisinvention. The mobile telephone and digital audio/video player of FIGS.13 a and 13 b can advantageously benefit from single-surface multi-touchsensor panel 1324 because only a single surface of circuitry is neededto realize a multi-touch sensor, reducing manufacturing costs and makingthe sensor panel very thin and flexible. Manufacturing costs may bereduced because no assembly steps are needed on the second side of thesubstrate, and because the components on the first side can be appliedusing low cost processes such as printing or rolling. Furthermore, theTFTs can be formed using inexpensive low mobility organic TFTs. Thesingle-surface multi-touch sensor panel is also lower in powerconsumption, and its projection scanning principles results in fastframe rates, a reduction in the memory needed to hold surface data, andsimpler data processing.

Although the present invention has been fully described in connectionwith embodiments thereof with reference to the accompanying drawings, itis to be noted that various changes and modifications will becomeapparent to those skilled in the art. Such changes and modifications areto be understood as being included within the scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A single-surface touch sensor panel, comprising: a plurality of distributed resistor-capacitor (RC) lines arranged in an array of rows and columns, the distributed RC lines including alternating connected transistors and metal pads formed on a single surface of a sensor panel substrate, each transistor having drain and source terminals connected to adjacent metal pads; a column enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a column; and a row enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a row.
 2. The single-surface touch sensor panel of claim 1, further comprising: one or more drivers couplable to both ends of every distributed RC line for driving a pulse through the distributed RC line in different directions; one or more comparators couplable to both ends of every distributed RC line for receiving the pulse from the distributed RC line; and pulse travel time measurement logic configured for measuring a travel time of each pulse as it passes through the distributed RC line.
 3. The single-surface touch sensor panel of claim 1, the transistors comprising thin-film transistors (TFTs).
 4. The single-surface touch sensor panel of claim 1, the transistors comprising organic thin-film transistors (TFTs).
 5. A single-surface touch-sensitive distributed resistor-capacitor (RC) array, comprising: alternating connected transistors and metal pads, each transistor having drain and source terminals connected to adjacent metal pads, the metal pads electrically coupled between the drain and source terminals of adjacent transistors, the transistors and metal pads formed in rows and columns on a single surface of a substrate; and a row enable line connected to a gate terminal of every transistor in the rows, and a column enable line connected to the gate terminal of every transistor in the columns.
 6. The single-surface touch-sensitive distributed RC line of claim 5, further comprising: one or more drivers couplable to both ends of the distributed RC line for driving a pulse through the distributed RC line in different directions; one or more comparators couplable to both ends of the distributed RC line for receiving the pulse from the distributed RC line; and pulse travel time measurement logic configured for measuring a travel time of each pulse as it passes through the distributed RC line.
 7. The single-surface touch-sensitive distributed RC line of claim 5, the transistors comprising thin-film transistors (TFTs).
 8. The single-surface touch-sensitive distributed RC line of claim 5, the transistors comprising organic thin-film transistors (TFTs).
 9. A method for forming a single-surface touch sensor panel, comprising: forming each of a plurality of distributed resistor-capacitor (RC) lines by alternating connected transistors and metal pads on a single surface of a sensor panel substrate, each transistor having drain and source terminals connected to adjacent metal pads; arranging the plurality of distributed RC lines in an array of rows and columns; connecting a column enable line to a gate terminal of every transistor in the distributed RC lines oriented in a column; and connecting a row enable line to a gate terminal of every transistor in the distributed RC lines oriented in a row.
 10. The method of claim 9, the distributed RC lines formed on the single surface of the sensor panel substrate by printing techniques.
 11. The method of claim 9, the transistors comprising thin-film transistors (TFTs).
 12. The method of claim 9, the transistors comprising organic thin-film transistors (TFTs).
 13. A method for forming a single-surface touch-sensitive distributed resistor-capacitor (RC) array, comprising: alternating connected transistors and metal pads in rows and columns on a single surface of a substrate, each transistor having drain and source terminals connected to adjacent metal pads, wherein the metal pads are electrically coupled between the drain and source terminals of adjacent transistors; and connecting a row enable line to a gate terminal of every transistor in the rows, and connecting a column enable line to the gate terminal of every transistor in the columns.
 14. The method of claim 13, the transistors and metal pads formed on the single surface of the substrate by printing techniques.
 15. The method of claim 13, the transistors comprising thin-film transistors (TFTs).
 16. The method of claim 13, the transistors comprising organic thin-film transistors (TFTs).
 17. A method for detecting one or more touches on a single-surface touch sensor panel having columns and rows of distributed resistor-capacitor (RC) lines formed from alternating transistors and metal pads on a single surface of a sensor panel substrate, comprising: for every row, enabling the transistors in that row while disabling the transistors in all columns, sending a pulse left-to-right and then right-to-left through the row, measuring left-to-right and right-to-left pulse travel times through the row, and computing an equalized pulse travel time for that row as the sum of the left-to-right and right-to-left travel times; for every column, enabling the transistors in that column while disabling the transistors in all rows, sending a pulse top-to-bottom and then bottom-to-top through the column, measuring top-to-bottom and bottom-to-top pulse travel times through the column, and computing an equalized pulse travel time for that column as the sum of the top-to-bottom and bottom-to-top travel times; and identifying the rows and columns having touches as those rows and columns having equalized pulse travel times greater than a no-touch equalized pulse travel time.
 18. The method of claim 17, wherein enabling transistors comprises turning on the transistors by applying a first potential at a gate terminal of the transistors, and disabling transistors comprises turning off the transistors by applying a second potential at the gate terminal of the transistors.
 19. The method of claim 17, wherein sending a pulse through the rows and columns comprises connecting drivers to the rows and columns and generating a pulse from the connected drivers, and connecting comparators to the rows and columns and detecting pulses received from the rows and columns at the connected comparators.
 20. The method of claim 19, wherein measuring pulse travel times comprises recording a first time when a pulse is generated by a driver and a second time when that pulse is detected by the comparator, and computing a difference between the first and second times.
 21. The method of claim 17, further comprising disambiguating touch locations by: for any two rows “i” and “j” at which a touch was detected, making a first comparison as to whether the right-to-left pulse travel time for row “i” is greater than the right-to-left pulse travel time for row “j”, making a second comparison as to whether the left-to-right pulse travel time for row “i” is greater than the left-to-right pulse travel time for row “j”, determining that the touch at row “i” is in a column to a left of the touch at row “j” if the first comparison is true and the second comparison is false, determining that the touch at row “i” is in a column to a right of the touch at row “j” if the first comparison is false and the second comparison is true, and determining that the touch at row “i” is in the same column as the touch at row “j” if the first and second comparisons are false; and for any two columns “k” and “m” at which a touch was detected, making a third comparison as to whether the top-to-bottom pulse travel time for column “k” is greater than the top-to-bottom pulse travel time for column “m”, making a fourth comparison as to whether the bottom-to-top pulse travel time for column “k” is greater than the bottom-to-top pulse travel time for column “m”, determining that the touch at column “k” is in a row below the touch at column “m” if the third comparison is true and the fourth comparison is false, determining that the touch at column “k” is in a row above the touch at column “m” if the third comparison is false and the fourth comparison is true, and determining that the touch at column “k” is in the same row as the touch at column “m” if the third and fourth comparisons are false.
 22. A method for detecting one or more touches on a single-surface touch-sensitive distributed resistor-capacitor (RC) line formed from alternating transistors and metal pads on a single surface of a substrate, comprising: enabling the transistors in the distributed RC line, sending a pulse left-to-right and then right-to-left through the distributed RC line, and measuring left-to-right and right-to-left pulse travel times through the distributed RC line; and computing a difference between the left-to-right and right-to-left travel times to determine the location of a single touch on the distributed RC line.
 23. A system for detecting one or more touches on a single-surface touch sensor panel having columns and rows of distributed resistor-capacitor (RC) lines formed from alternating transistors and metal pads on a single surface of a sensor panel substrate, the system including a processor programmed for causing performance of a method comprising: for every row, enabling the transistors in that row while disabling the transistors in all columns, sending a pulse left-to-right and then right-to-left through the row, measuring left-to-right and right-to-left pulse travel times through the row, and computing an equalized pulse travel time for that row as the sum of the left-to-right and right-to-left travel times; for every column, enabling the transistors in that column while disabling the transistors in all rows, sending a pulse top-to-bottom and then bottom-to-top through the column, measuring top-to-bottom and bottom-to-top pulse travel times through the column, and computing an equalized pulse travel time for that column as the sum of the top-to-bottom and bottom-to-top travel times; and identifying the rows and columns having touches as those rows and columns having equalized pulse travel times greater than a no-touch equalized pulse travel time.
 24. The system of claim 23, wherein enabling transistors comprises turning on the transistors by applying a first potential at a gate terminal of the transistors, and disabling transistors comprises turning off the transistors by applying a second potential at the gate terminal of the transistors.
 25. The system of claim 23, wherein sending a pulse through the rows and columns comprises connecting drivers to the rows and columns and generating a pulse from the connected drivers, and connecting comparators to the rows and columns and detecting pulses received from the rows and columns at the connected comparators.
 26. The system of claim 25, wherein measuring pulse travel times comprises recording a first time when a pulse is generated by a driver and a second time when that pulse is detected by the comparator, and computing a difference between the first and second times.
 27. The system of claim 23, the method further comprising disambiguating touch locations by: for any two rows “i” and “j” at which a touch was detected, making a first comparison as to whether the right-to-left pulse travel time for row “i” is greater than the right-to-left pulse travel time for row “j”, making a second comparison as to whether the left-to-right pulse travel time for row “i” is greater than the left-to-right pulse travel time for row “j”, determining that the touch at row “i” is in a column to a left of the touch at row “j” if the first comparison is true and the second comparison is false, determining that the touch at row “i” is in a column to a right of the touch at row “j” if the first comparison is false and the second comparison is true, and determining that the touch at row “i” is in the same column as the touch at row “j” if the first and second comparisons are false; and for any two columns “k” and “m” at which a touch was detected, making a third comparison as to whether the top-to-bottom pulse travel time for column “k” is greater than the top-to-bottom pulse travel time for column “m”, making a fourth comparison as to whether the bottom-to-top pulse travel time for column “k” is greater than the bottom-to-top pulse travel time for column “m”, determining that the touch at column “k” is in a row below the touch at column “m” if the third comparison is true and the fourth comparison is false, determining that the touch at column “k” is in a row above the touch at column “m” if the third comparison is false and the fourth comparison is true, and determining that the touch at column “k” is in the same row as the touch at column “m” if the third and fourth comparisons are false.
 28. A system for detecting one or more touches on a single-surface touch-sensitive distributed resistor-capacitor (RC) line formed from alternating transistors and metal pads on a single surface of a substrate, the system including a processor programmed for causing performance of a method comprising: enabling the transistors in the distributed RC line, sending a pulse left-to-right and then right-to-left through the distributed RC line, and measuring left-to-right and right-to-left pulse travel times through the distributed RC line; and computing a difference between the left-to-right and right-to-left travel times to determine the location of a single touch on the distributed RC line.
 29. An apparatus for detecting one or more touches on a single-surface touch sensor panel having columns and rows of distributed resistor-capacitor (RC) lines formed from alternating transistors and metal pads on a single surface of a sensor panel substrate, comprising: means for enabling the transistors in every row while disabling the transistors in all columns, means for sending a pulse left-to-right and then right-to-left through each row, means for measuring left-to-right and right-to-left pulse travel times through each row, and means for computing an equalized pulse travel time for each row as the sum of the left-to-right and right-to-left travel times for each row; means for enabling the transistors in every column while disabling the transistors in all rows, means for sending a pulse top-to-bottom and then bottom-to-top through each column, means for measuring top-to-bottom and bottom-to-top pulse travel times through each column, and means for computing an equalized pulse travel time for each column as the sum of the top-to-bottom and bottom-to-top travel times for each column; and means for identifying the rows and columns having touches as those rows and columns having equalized pulse travel times greater than a no-touch equalized pulse travel time.
 30. An apparatus for detecting one or more touches on a single-surface touch-sensitive distributed resistor-capacitor (RC) line formed from alternating transistors and metal pads on a single surface of a substrate, comprising: means for enabling the transistors in the distributed RC line, means for sending a pulse left-to-right and then right-to-left through the distributed RC line, and means for measuring left-to-right and right-to-left pulse travel times through the distributed RC line; and means for computing a difference between the left-to-right and right-to-left travel times to determine the location of a single touch on the distributed RC line.
 31. A mobile telephone including a single-surface touch sensor panel, the single-surface touch sensor panel comprising: a plurality of distributed resistor-capacitor (RC) lines arranged in an array of rows and columns, the distributed RC lines including alternating connected transistors and metal pads formed on a single surface of a sensor panel substrate, each transistor having drain and source terminals connected to adjacent metal pads; a column enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a column; and a row enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a row.
 32. A digital audio player including a single-surface touch sensor panel, the single-surface touch sensor panel comprising: a plurality of distributed resistor-capacitor (RC) lines arranged in an array of rows and columns, the distributed RC lines including alternating connected transistors and metal pads formed on a single surface of a sensor panel substrate, each transistor having drain and source terminals connected to adjacent metal pads; a column enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a column; and a row enable line connected to a gate terminal of every transistor in the distributed RC lines oriented in a row. 